Quiet attenuator system utilizing relay activated photosensitive resistors



Aug 25, 1970 F. w. MAczKA 3,525,926

. QUIET ATTENUATQE. SYSTEM UTILIZING RELAY ACTIVATED PHOTOSENSITIVE RESISTORS Filled May s, 1968 @i 'm ""I' fdl s@ VQ al) & vq Q QQ@ @E g un mi Q. n Em u@ @ME I Y E* Q l NN l 1 m k -Ill' 'Q EN: 1

\ f/I W //atza INVENTOR. `)sncfwg/- United States Patent O 3,525,926 QUIET AT'IENUATOR SYSTEM UTILIZING RELAY ACTIVATED PHOTOSENSITIVE RESISTORS Frank W. Maczka, Rockville, Md., assigner, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed May 3, 1968, Ser. No. 726,302 Int. Cl. G05f 5/00 U.S. Cl. 323-21 3 Claims ABSTRACT OF THE DISCLOSURE A quiet attenuator system wherein a plurality of relay operated attenuator ladder networks provide audio attenuation over a Iwide range with smooth transition switching 'between levels being accomplished by energizing and BACKGROUND OF THE INVENTION This invention relates to the art of signal attenuation and more particularly to variable attenuation means which are particularly suited to use in simulation apparatus for example for the simulation of operational sonar equipment, although the system is also suited to use in other applications.

Variable attenuators, particularly logarithmic attenuators, have been used for the purpose of simulating natural attenuation of sonar signals and have utilized relays to direct audio signals through selected attenuator pads or resistors of differing values to produce a step-by-step approximation of logarithmic attenuation. That technique, however reliable and inexpensive to construct and maintain, has had the serious disadvantage of audibly distinct switching transients which, when utilized in simulation applications, detracts appreciably from the realism of the simulation.

Other approaches, such as servo-controlled Ivariable attenuators, are expensive and difficult to maintain and, like solid state approaches, are characterized by limited dynamic range.

SUMMARY OF THE INVENTION With the foregoing in mind, it is a primary object of the present invention to provide an improved variable attenuator system of the type utilizing attenuator means which vary in a step-by-step manner, such as relay operated ladder networks of discrete attenuator pads or elements, but .which system provides smooth transition between selected values of attenuation, whereby an attenuated audio signal is free of distinct, audible clicks or transitions.

As another object this invention aims to accomplish the foregoing through the provision of an attenuator system comprising a novel combination of a plurality of attenuator networks which can be operated by steps to different values as `by relays or other switching means, a photoresponsive resistive means connected between each of the attenuator networks and a common output line, a filament means associated with each of the photo-responsive resistance means, and switching means for alternatively energizing and dev-energizing the filament means whereby the relatively slow turn-on and slower turn-off thereof causes the resistive means to effect a correspondingly smooth transition between attenuated signal levels at the output line.

BRIEF DESCRIPTION OF THE DRAWING Other objects and advantages of the invention will be- ICC come apparent from the following description of a presently preferred embodiment thereof when read in conjunction with the accompanying sheet of drawings forming a part of this specification, and wherein the sole view is a diagrammatic illustration of a quiet logarithmic attenuator system embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In form` of the invention illustrated in the drawing and described hereinafter there is provided an improved, quiet logarithmic attenuator system, generally indicated at 10. The system 10` comprises a pair of attenuator ladder networks 12 and 14. The networks 12 and 14 may be of any conventional construction wherein the attenuation factor is varied in a step-by-step manner. The preferred form conveniently comprises a network of attenuator pads (which may be resistors) and relay means for selectively combining the attenuator pads to provide desired attenuation factors.

In the present example audio signals to be attenuated are provided 4by an audio signal source 16 and are conducted as an input to each of the attenuator networks 12 and 14 as shown by lines 18` and 20.

The audio signal source 16 may, for example, provide pings of audio frequency representative of sonar signals for simulation purposes in a sonar training device wherein the attenuator system 10 iis provided toattenuate the output of these audio signals logarithmically to simulate natural attenuation of sonar signals. As such it is controlled via line 2-2 by a simulation computer 24 which forms no actual part of the invention.

The relays of the attenuator networks 12 and 14 are actuated in predetermined sequences by a relay driver 26 via lines 28, 30 in response to control signals from the simulation computer 24 via line 32 coordinating the relay drive logic with the generation of the audio signals. The relay driver 26 may comprise binary logic means, rotary switch means, or any other drive signal sequencing means suitable to the application of the system 10.

In any event, the relay driver up-dates the attenuator networks 12 and 14 in an alternative manner for a purpose which will become apparent as the description proceeds.

The attenuated audio signal outputs of the attenuator networks 12 and 14 appear on lines 34 and 36, respectively, which are connected through photo-responsive resistive elements 42 and 44, respectively, to a common output line 46.

Associated with the photo-responsive resistive elements 42 and 44 are filament means 48 and 50, respectively. The filaments 48 and 50 may form part of individual incandescent lamps. However, each filament may be enclosed with its associated photo-resistive element by a sealed envelope to form a unitary package, one example of which is sold under the name Raysistor. Thus, thefilament 48 is shown associated with the resistive element 42 within an envelope 52, and the filament 50 is shown associated with the resistive element 44 within an envelope 54. Energization of the filaments 48 and 50 is acc0mplished alternatively by a switching relay 60 which is under the control of the relay driver26 via line 62. Relay 60 includes a contractor 60a movable between contacts 60b and 60e` by a solenoid 60d.

When the contactor is in the illustrated position, a circuit may be traced from a filament voltage source 64 through a conductor 66, contactor 60a, contact 60b, a conductor 68, filament means 48, and conductor 70 to ground and return to source 64. When the solenoid 60d is energized the contactor 60a moves to Ibreak the just described circuit and completes a circuit which may be traced from the filament voltage supply 64 through con- 3 ductor 66, contactor 60a, contact 60C, a conductor 72, the filament S0, and conductor 74 to ground.

Energization of the filaments 48 and 50 produces radiant energy which falls upon the respective resistive elements 42 and 44, the resistances of which decrease markedly in response to the radiant energy. Because of the relatively slow turn-on of a filament (time to come to steady emission of light or radiant energy) and slower turn-off thereof, the attendant decreases and increases in resistance of the associated element 42 0r 44 will be correspondingly gradual. Itis this characteristic which the invention employs to eliminate audible clicks in the attenuated audio output on line 46.

To this end, energization and de-energization of the switching relay 60 is effected by the relay driver 26 in timed relation to the alternative up-dating of the attenuator ladder networks 12 and 14 by the relay driver. Thus, when the relay is in its illustrated position with filament 48 fully energized, the resistive element 42 presents its least resistance and the audio signal from source 16, which is attenuated to a predetermined level by the ladder network 12, is passed with minimum diminution by the resistive element to the output line 46. A suitable load resistor 76 is provided ybetween the line 46 and ground, and the output of the system appears as a voltage signal thereacross which signal may be taken from the output terminal 78.

At this time the relay driver, via line 30, causes the attenuator ladder network 14 to be up-dated to provide an attenuation factor which may be substantially different from that presently provided by the network 12 and which may be substantially different from its own immediately pre-existing state. Now, the relay driver 26 causes the contactor 60a to move away from the contact 60b and against the contact 60C. Thereupon, the radiation by filament 48 decays gradually (as compared to the time taken to change the relay contacts) and the resistive element 42 becomes effective at a corresponding rate to essentially completely impede the passage of the attenuated signal from the network 12. At the same time, the filament 50 begins to radiate and the resistive impedance of the element 44 to the attenuated signal on line 36 from the network 14 gradually falls and allows that signal to pass to the output line 46.

Because of the gradual changes in resistivity of the resistive elements 42 and 44, the change in the attenuated signal reaching lineY 46 by virtue of the different attenuation factor of network 14 with respect to network 12, is smooth. Accordingly, no audible transition click is heard when the signal is used as a simulated sonar signal. At the time when the resistive impedance of the element 42 is greatest, the relay driver 26 causes the attenuator ladder network 12 to be up-dated to provide an attenuation factor which may be substantially different than its own immediately pre-existing factor and different from that existing in the network 14. Because the impedance of the resistive element 42 is at this time at a maximum, there will be no audible click resulting from transients common to relays, switches or the like within the network 12, nor from the rapid change of attenuation factor therein.

The process is then carried forth with the operation of the relay 60 to de-energize the filament 50 and to energize the filament 48.

By properly programming the operation of the relay driver 26, the system can vary the attenuation of a signal over a wide range in a smooth manner with the attenuated signal being free of audible clicks resulting from steps of attenuation level.

It will be recognized, of course, that the attenuator ladder networks 12 and 14 could be replaced by other stepping networks wherein the stepping is achieved by other switching means than relays, for example switching transistors. It will also be recognized that the switching function of relay 60 could as well be performed by other switching means such as a bistable Hip-flop. In the event of these alternatives, the relay driver 26 would, of course, be replaced by a suitable driver for the types of switching elements selected.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A variable attenuator system comprising:

first and second attenuator means having a common input for receiving a signal to be attenuated, said second attenuator means being operative to provide a different attenuation factor than said first attenuator means;

said first and second attenuator means each comprising means for varying the attenuation factor thereof in a step-by-step manner;

a first radiant energy responsive resistive element connected between said first attenuator means and an output connection;

a second radiant energy responsive resistive element connected between said second attenuator means and said output connection;

said radiant energy responsive resistive elements comprising photo-responsive elements;

first and second filament means associated with said first and second resistive elements respectively;

a source of filament voltage;

said first and second filament means comprising incandescent lamp filaments which emit light energy when energized;

switching means connected between said source of filament voltage and said filament means for alternatively energizing and de-energizing said first and Seccond filament means;

drive means connected to said first and second attenuator means and to said switching means;

said drive means being operative to effect alternative up-dating of the attenuation factors of said first and second attenuation means; and

said drive means -being operative to effect said alternative energization and de-energization of said first and second filament means in timed relation to the updating of said attenuator means, whereby said first attenuator means is up-dated when the resistive impedance of said first resistive element is at or near its maximum, and said second attenuator means is 11p-dated when the resistive impedance of said second resistive element is at or near its maximum.

2. A variable attenuator system as defined in claim 1,

and wherein: said first and second attenuator means each comprise a relay operated attenuator ladder network.

3. A variable attenuator system as defined in claim 2, and wherein: said switching means comprises relay means.

Wildberger 323- J D MILLER, Primary Examiner A. D. PELLINEN, Assistant Examiner U.S. Cl. X.R. 

